When a patient is suffering from injury to an anterior cruciate ligament which has not been surgically treated, the ligament disintegrates after a time, and at its attachment to the femur between both the femoral condyles thereof, a bony excrescence or osteophyte is formed. On remaking the joint, i.e. a surgical operation for fitting a new ligament, the osteophyte must first be removed with a chisel or the like, to recreate the normal space for the new ligament. The distance between the femoral condyles should normally be 21 mm, but may have decreased to about 11 mm due to the ostephyte.
To obtain the correct distance between the femoral condyles the distance must be measured continuously as the osteophyte is removed. So far, this has been done by using a forceps, which has been inserted between the femoral condyles so that the legs of the forceps have come into engagement against the inside of the respective condyle, after which the forceps has been removed while maintaining the distance between its legs, and this distance has been measured with the aid of a ruler.
Other devices that have been used for making the measurement are vernier calipers and angularly bent wires.
Accurate measurement cannot be made with the known devices. In addition, forceps and vernier calipers take up large space and require that a relatively large opening is made to the space inside the joint.